The process of production and recovery of hydrogen by steam and/or air reforming of hydrocarbon rich fuels is known in the art. Typical commercial sources for the production of hydrogen include steam reforming or partial oxidation of various hydrocarbon fuels, both liquid and gaseous. Common reforming techniques are carried out by reacting the hydrocarbon fuel with steam and/or with air or oxygen-enriched air, producing a hydrogen gas-containing syngas stream, which also typically may contain non-hydrogen components comprising carbon monoxide, carbon dioxide, water, residual hydrocarbon fuel or nitrogen. Typically in conventional hydrogen production systems, carbon monoxide in the syngas stream may be at least partially converted to carbon dioxide by means of the water gas shift reaction to increase the content of hydrogen in the syngas stream, while reducing the content of carbon monoxide (may be reduced to as low as about 1% CO in reformate after typical high and low temperature water gas shift reactions). Conventionally this water gas-shifted syngas stream is then sent to a PSA unit for purification of the hydrogen component to produce a hydrogen-rich product gas.
Conventional PSA systems such as are known in the art may be employed for the purification of the hydrogen component of a reformate syngas stream to provide a hydrogen-rich product gas. Such conventional PSA systems typically function by passing a multi-component feed gas mixture through multiple adsorber beds (each comprising at least one adsorbent material) in a progressive cyclic phase, adsorbing at least one relatively strongly adsorbed component at an elevated pressure, while at least one relatively weakly adsorbed component passes through the bed to be delivered as an enriched product gas. In the case of hydrogen production from reformate syngas streams, such relatively weakly adsorbed component typically comprises hydrogen gas. Following the above described adsorption step, adsorbers in a conventional PSA system are typically depressurized in one or more steps, during which enriched product gas may be further extracted from the adsorber, typically followed by countercurrent desorption and purge prior to resuming the next cyclic feed or adsorption step of the adsorber. Exemplary publications disclosing such conventional PSA systems may include U.S. Pat. Nos. 3,564,816 to Batta and U.S. Pat. No. 3,986,849 to Fuderer et. al.
An expanding field of application for enriched hydrogen use is as fuel for fuel cell power generation systems. In particular, PEM type fuel cells, a major type of fuel cell developed for power generation, automotive and other uses, require enriched hydrogen as a fuel, and particularly require hydrogen fuel with low carbon monoxide levels (typically less than about 50 ppm by volume) to avoid poisoning the fuel cell, which is very sensitive to contamination by carbon monoxide. Preferential oxidation reactors are known in the art for use to reduce the carbon monoxide concentration of reformate gas streams to levels suitable for use in some PEM type fuel cell systems, however some such preferential oxidation reactors are limited by the relatively long startup and response times required for the reactor to react to changes in the reformate stream. PSA is also known for use to purify reformate synthesis gas to reduce carbon monoxide levels in an enriched hydrogen fuel gas suitable for PEM fuel cell use.
In order to reduce the capital cost and physical size of PSA systems, it is known in the art to employ rapid cycle PSA to reduce the required adsorber volume (and therefore the size and cost of the PSA) to produce a desired volume of enriched hydrogen product gas in a given time (known as bed size factor or BSF, which may be expressed in units of volume of adsorber/volume of product gas produced/second). Such rapid PSA cycles as disclosed in U.S. Pat. No. 6,660,064 to Golden et. al. are claimed to provide enriched hydrogen product gas from reformate syngas according to computer simulations of pressure swing adsorption using known granular carbon adsorbent materials. The disclosed pressure swing adsorption system is capable to operate at cycle speeds up to approximately 1.3 cycles per minute (corresponding approximately to 45 second cycle durations with as low as 15 second feed intervals). The relatively short response times of such rapid cycle PSA systems to changes in the reformate feed gas stream, in comparison to non-adsorptive alternative systems such as preferential oxidation reactors, may provide an advantage for use in fuel cell systems where start/stop, or other changes in the reformate feed to the purification system may occur.
Despite the developments in the art noted above, it is desired to provide improved rapid cycle PSA systems for producing enriched hydrogen product gas from reformate syngas mixtures.